The ivory barnacle, Balanus eburneus, is a medium-sized sessile barnacle belonging to the class Cirripedia. This group contains approximately 900 described species, about two-thirds of which are free-living barnacles that foul or attach to rocks and other hard intertidal and submerged surfaces (Ruppert & Barnes 1994). Like other members of the suborder Balanomorpha, the soft tissue of B. eburneus is protected within a series of rigid plates, known as capitular plates. The solid white plates of the ivory barnacle form a conical appearance that is largest at the base, with a diamond-shaped opening guarded by a movable opercular lid composed of two symmetrical triangular halves (eg. Gosner 1978). Each of these halves contains two plates, the tergum and the scutum. During feeding, excretion, larval release and copulation, the operculum opens as the terga and scuta are flexed out to the sides.